The hunt for leptoquarks is on

A collision event recorded by CMS at the start of the data-taking run of 2018. CMS sifts through such collisions up to 40 million times per second looking for signs of hypothetical particles like leptoquarks. Credit: Thomas McCauley/Tai Sakuma/CMS/CERN

Matter is made of elementary particles, and the Standard Model of particle physics states that these particles occur in two families: leptons (such as electrons and neutrinos) and quarks (which make up protons and neutrons). Under the Standard Model, these two families are totally distinct, with different electric charges and quantum numbers, but have the same number of generations (see image below).

However, some theories that go beyond the Standard Model, including certain "grand unified theories," predict that leptons and quarks merge at high energies to become leptoquarks. These leptoquarks are proposed in theories attempting to unify the strong, weak and electromagnetic forces.

Such "unifications" are not unusual in physics. Electricity and magnetism were famously unified in the 19th century into a single force known as electromagnetism, via Maxwell's elegant mathematical formulae. In the case of leptoquarks, these hybrid particles are thought to have the properties of both leptons and quarks, as well as the same number of generations. This would not only allow them to "split" into the two types of particles but would also allow leptons to change into quarks and vice versa. Indeed, anomalies detected by the LHCb experiment as well as by Belle and Babar in measurements of the properties of B mesons could be also explained by the existence of these hypothesised particles.

If leptoquarks exist, they would be very heavy and quickly transform, or "decay," into more stable leptons or quarks. Previous experiments at the SPS and LEP at CERN, HERA at DESY and the Tevatron at Fermilab have looked at decays to first- and second-generation particles. Searches for third-generation leptoquarks (LQ3) were first performed at the Tevatron, and are now being explored at the Large Hadron Collider (LHC).

Since leptoquarks would transform into a lepton and a quark, LHC searchers look for telltale signatures in the distributions of these "decay products." In the case of third-generation leptoquarks, the lepton could be a tau or a tau neutrino while the quark could be a top or bottom.

The Standard Model of particle physics divides elementary particles of matter into separate families: leptons and quarks. Each family consists of six particles, which are related in pairs, or "generations." The lightest and most stable particles make up the first generation, whereas the heavier and less stable particles belong to the second and third generations. The six leptons are arranged in three generations – the "electron" and the "electron neutrino," the "muon" and the "muon neutrino," and the "tau" and the "tau neutrino."The six quarks are similarly paired in three generations – the "up quark" and the "down quark" form the first generation, followed by the "charm quark" and "strange quark," then the "top quark" and "bottom (or beauty) quark." Credit: Daniel Dominguez/CERN

In a recent paper, using data collected in 2016 at a collision energy of 13 TeV, the Compact Muon Solenoid (CMS) collaboration at the LHC presented the results of searches for third-generation leptoquarks, where every LQ3 produced in the collisions initially transformed into a tau-top pair.

Because colliders produce particles and antiparticles at the same time, CMS specifically searched for the presence of leptoquark-antileptoquark pairs in collision events containing the remnants of a top quark, an antitop quark, a tau lepton and an antitau lepton. Further, because leptoquarks have never been seen before and their properties remain a mystery, physicists rely on sophisticated calculations based on known parameters to look for them. These parameters include the energy of the collisions and expected background levels, constrained by the possible values for the mass and spin of the hypothetical particle. Through these calculations, the scientists can estimate how many leptoquarks might have been produced in a particular data set of proton-proton collisions and how many might have been transformed into the end products their detectors can look for.

"Leptoquarks have became one of the most tantalising ideas for extending our calculations, as they make it possible to explain several observed anomalies. At the LHC we are making every effort to either prove or exclude their existence," says Roman Kogler, a physicist on CMS who worked on this search.

After sifting through collision events looking for specific characteristics, CMS saw no excess in the data that might point to the existence of third-generation leptoquarks. The scientists were therefore able to conclude that any LQ3 that transform exclusively to a top-tau pair would need to be at least 900 GeV in mass, or around five times heavier than the top quark, the heaviest particle we have observed.

The limits placed by CMS on the mass of third-generation leptoquarks are the tightest so far. CMS has also searched for third-generation leptoquarks that transform into a tau lepton and a bottom quark, concluding that such leptoquarks would need to be at least 740 GeV in mass. However, it is important to note that this result comes from the examination of only a fraction of LHC data at 13 TeV, from 2016. Further searches from CMS and ATLAS that take into account data from 2017 as well as the forthcoming run of 2018 will ensure that the LHC can continue to test theories about the fundamental nature of our universe.

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17 comments

RUNII: No SUSY, No WIMP, No HIGGS, No NEW PHYSICS?http://vixra.org/...40v5.pdfhttps://www.econo...ysicists"Whether politicians and taxpayers will be up for this remains to be seen. That fundamental physics has got as far as it has is, essentially, a legacy of its delivery to political leaders of the mid-20th century of the atom and hydrogen bombs. The consequence of this was that physicists were able to ask for expensive toys—for who knew what else they might come up with. That legacy has now been spent, though, and any privilege physics once had has evaporated. This risks leaving in permanent limbo not only the GUTs and their brethren, but also the sceptical idea of Dr Hossenfelder that the Standard Model really is all there is. And that would surely be the most depressing result of all."?

Excellent statement gunnqu. The record shows that I have from the very earliest days of being able to make comments about CERN's results, lodged the opinion that; 'No useful information can be drawn from the collision of two like particles.' The reasoning behind my statement, coming from the fact that it cannot be determined where the resultant particles have come from. (either singly or otherwise.) Without such precise determination the evidence is deeply flawed. (In my view.) (And I'm wide open to any other interpretations.)

So, we should have never done the same with electron microsocopy (which pretty much enabled the development of the transistor...which is the only reason dumb people like you can spew nonsense on the internet)?

"So, we should have never done the same with electron microsocopy (which pretty much enabled the development of the transistor...which is the only reason dumb people like you can spew nonsense on the internet)?"

Manipulating stable particles in new and creative ways is science. Useful information that enables us to do this is not coming from anything happening at CERN. Is it an engineering marvel to accelerate Ions to relativistic speeds and actually hit another target? Yes, do the results mean what is claimed? Only if you believe what is claimed. As mentioned above...the money stops when the "new findings" do....so they have to claim something is being discovered to keep the funding coming.

"Follow the money."Good advice disregarded by above cranks disgruntled that no one is willing to buy their woo.

Those "billions" the woo merchants are drooling after? Are a combination of Public Funding, founder/alumni endowments to educational institutions, private foundation grants & corporate investment in research programs.

Cranks seem to share the same delusion that money invested in real science, is stuffed into a rocket as propellant and shot off into space! To vanish forever.

The narrow minded cannot comprehend that investing in research is not like putting kindling into a stove. Money spent on an expensive piece of equipment?

Some of that pays the salary of the truck driver who delivers the new gear to the laboratory. His wife pays for groceries that pay the salary of the checkout clerk. Who in turn buys himself a beer at his favorite bar. The guy paid to mop the barroom floor is paid from those "billions". Supports his efforts to sell woo on Phys.org.

Oh hype, there are few things humans do that are more illogical than money! Be very difficult to invent any new human endeavor crazier, more sarcastic of intellectual comprehension than our Modern Economy.

I believe there was an article on this site. About how efficient is was for ants to search for food, utilizing the stochastic, method. The infamous "drunkard''s walk".

So, for all our big brain bombast, we really are no smarter than a single, hungry ant?

Two fun, pop books (that I have no financial interest) I would recommend are:"Dollar" by Jason Goodwinand "Blackbeard" by Samuel Marquis

Both books approach the founding of Modern America as business ventures from different directions.

And can assist you in clarifying your assessment of the activities of the Wall Street Casinos.

When god sits upon the throne? All the world and all the people are the personal property of the the deified. I'll bet you don't pay your wife to scrub the skid marks out of your shorts.

The very concept of Human Rights is still novel to the Human Race. Another bet I'd cover? Is, given a real, unpunished choice? A large percentage of Humanity would still prefer acquiescence to authority over the uncertainty of Free Will!

OK, lets make sense. Your imaginary God does not exists. God, denied God and told you the sun gives life, and the stars may be other suns. He did not use money and pointed out that we all have a conscience and should treat each other as brothers.

Yes, God knew about particles; but, particles don't exist. Not what He was talking about.W/ Logic its obvious.